Tangential flow pumping channel for turbomolecular pumps

Abstract: The present invention relates to turbomolecular pumps comprising one or more tangential flow pumping stages in addition to axial flow pumping stages, so as to raise the pump exhaust pressure up to the atmospheric pressure, wherein at least one tangential flow pumping stage has a tangential flow pumping channel of improved design. The channel is located between the lateral surface of the rotor disk (5) and the annular inner wall of stator (2) and comprises an upper closure plate (3) provided with suction port (9) and a lower closure plate (4) provided with discharge port (1⊘) wherein these ports are operably coupled to the tangential flow pumping channel (1) . The cross-section area of the channel is enlarged from its periphery portion defined by the lateral surface of the rotor disk (5) to a central portion defined by the upper and lower closure plates (3,4) .

Description: Field of the Invention The present invention relates to a tangential flow pumping channel of improved design for turbomolecular pumps. In particular it relates to a tangential flow pumping channel utilizing one or more tangential flow pumping stages in conjunction with axial flow pumping stages. Background of the Invention Tangential flow pumping stages have previously been incorporated in turbomolecular pumps, an example of which is disclosed in European Patent Application Publication No.EP. ⊘,445,855 assigned to the applicant of the present application. The cited '855 publication pertains to a turbomolecular pump which, in addition to conventional axial flow pumping stages, utilizes one or more tangential flow pumping stages, wherein the stator ring surrounding the rotor disk and the rotor disk surfaces are substantially parallel, thereby defining a pumping channel therebetween of substantially rectangular cross-section and uniform width. Research carried out testing the operational characteristics of the tangential channels of the aforementioned pumps has shown that the enlarged modifications of the rectangular cross-section of the pumping channel lead to the impressive results in terms of pumping speed compression ratio. Accordingly, one of the advantages of the present invention is a tangential flow pumping channel of improved design, as part of one or more tangential flow pumping stages in an axial flow turbomolecular pump, which is designed to substantially improve the above-identified operational characteristics of said turbomolecular pump. A further advantage of the present invention is a pumping channel of improved design as an element of a turbomolecular pump which can be easily manufactured at a low cost. Summary of the Invention In accordance with the present invention these advantages are achieved with the features of the characterizing portion of independent claims 1 to 3. The present invention provides a turbomolecular pump comprising a tangential flow pumping stage and axial flow pumping stage wherein the tangential flow pumping stage has a flow channel located between an annular grooved inner wall of a stator and a lateral portion of a rotor disk. The lateral surface of the rotor disk may be grooved. The flow channel has a central portion defined by an upper and lower closure plates with a suction and discharge ports respectively, and a periphery portion defined by the lateral surface of the rotor disk and the annular grooved inner wall of the stator the suction and discharge ports operably coupled to the tangential flow channel. Wherein a cross-sectional area of the channel is enlarged from the periphery to the central portion. The tangential flow pump further comprising a baffle. The upper closure plate and a first plane surface of the rotor disk facing this upper plate defining a first region of close tolerance between discharge port and suction port while the lower closure plate and a second plane surface of the rotor disk opposed to the first one and facing the lower closure plate defining a second region of close tolerance between the discharge and suction ports. The baffle is protruded from the plates, extending into the groove of the rotor disk and forming a third region of close tolerance therewith. Brief Description of the Drawings The invention will now be described in greater detail hereinafter relative to non-limitative embodiments, with reference to the accompanying drawings, in which: FIG.1 is a schematic view in axial section showing the channel of the present invention in a first embodiment; FIG.2 is a schematic view in axial section showing the channel of the present invention in a second embodiment; FIG.3 is a schematic view in axial section showing the channel of the present invention in a third embodiment; FIG. 4 is a partially broken perspective view of a part of a turbomolecular pump housing having a tangential pumping stage and a pumping channel according to the embodiment of FIG.1 . Detailed Description of the Invention A first embodiment of the present invention is depicted in FIG.1 and FIG.4 , wherein a pumping channel 1 of circular cross-section is formed in a tangential pumping stage within the walls of a stator 2 , consisting of a first upper closure plate 3 and a second lower closure plate 4 , and having a rotor disk 5 secured to a shaft 6 and positioned between said upper closure plate 3 and lower closure plate 4 . The area between the upper and lower closure plates and the first upper plane and second lower plane surfaces of rotor disk 5 thereby defines a first and second region 7 and 8 respectively, of close tolerance between said closure plates and the rotor disk. Upper closure plate 3 and lower closure plate 4 are joined together by suitable means known to those skilled in the art, an example of which is shown in the figure which depict the coupling of downwardly extending edge 19 of upper closure plate 3 with the upwardly extending edge 2⊘ of lower closure plate 4 . The upper and lower closure plates are further provided with a suction port 9 and a discharge port 1⊘ respectively, both in fluid communication with channel 1 . The interior wall surface 13 , formed by the junction of said plate edges 19 and 2 ⊘, has a substantially semicircular internal perimeter thereby forming a circular passageway when cooperating with a substantially semicircular groove 12 provided in the peripheral edge of rotor disk 5 . Channel 1 is partially closed by baffle 18 which extends from plate edges 19 and 2⊘ between discharge port 1⊘ and suction port 9 counterclockwise, according to the direction of rotation of shaft 6 , as indicated by arrow 21 , wherein baffle 18 protrudes towards rotor disk 5 , thus penetrating into groove 12 and forming a third region of close tolerance 11 therewith. In FIG.4 a pump housing 22 is shown comprising, in addition to a tangential flow pumping stage having a pumping channel according to the present invention, an axial flow pumping stage 23 is provided, equipped with a vane rotor 24 and a vane stator 25 . Referring now to FIG.2 there is shown a first modified embodiment of the present invention. The essential difference between this modified embodiment and the embodiment depicted in FIG.1 is that a rotor 26 , having a plane lateral surface for a peripheral edge, is provided instead of a rotor with a semicircular groove. In this modified embodiment, the lateral surface thereby defines channel 32 of substantially semicircular cross-section rather than a channel of substantially circular cross-section as was provided in the previous embodiment. In this embodiment identical components have been given the same reference numerals as those shown in FIG.1 . The advantages of the present invention's use of a pumping channel having a circular or semicircular cross-sectional area are particularly evident in molecular flow. Under molecular flow conditions we can assume for the pumping speed S the following relation: S≈A·V s where A is the cross-sectional area of the pumping channel; and where V s is the velocity averaged along the stator and rotor walls, and shown to be adversely proportional to the pumping channel perimeter, according to the following relation: V s = ∮ v•dL ∮ dL where L is the pumping channel perimeter and V is the velocity of a perimeter element dL in the axial direction. It is well known from common Euclidean geometry that for two figures having the same area A but different shape, the perimeter is at a minimum when the shape is circular. Therefore it can be easily understood from the above geometric relationship that V s and S are maximized by choosing a circular shape for the stationary part of the perimeter L, and V s is further increased by grooving the edge of the rotor as for example with a semicircular groove. A further consideration in the design of turbomolecular pumps regards the relative position of the moving surface of the rotor i.e., the peripheral wall with respect to stator wall. It is well known that the more the rotor penetrates the pumping channel, the more the value V s is increased, while conversely the less the rotor penetrates the pumping channel the more the channel cross-sectional area A increases. Based on these operational constraints it has been found that the best performances for the pumping of the present invention are achieved by utilizing a circular channel section obtained by means of a semicircular stator surface cooperating together with an opposing grooved rotor surface as disclosed above. Referring now to FIG. 3 a further embodiment is disclosed which is a less expensive alternative solution utilizing a partially optimized channel. In FIG.3 there is shown a channel 27 of substantially semicircular cross-section obtained by means of a semicircular groove 12 in the peripheral wall of rotor 5 . The downwardly extending edge 28 of upper closure plate 3⊘ and the upwardly extending edge 29 of lower closure plate 31 in stator 15 provide for a substantially rectangular shape for internal surface 14 of channel 27 , thereby forming a semicircular pumping channel having a larger moving surface.

Claims: A turbomolecular pump having a tangential flow pumping stage and axial flow pumping stage, said tangential flow pumping stage comprising: a rotor disk (5) secured to a pump shaft (6) and a stator (2) , said stator having an annular grooved inner wall receiving a lateral portion of said rotor disk (5) ; said lateral portion of said rotor disk (5) and said annular grooved inner wall of said stator (2) defining a flow channel (1) ; an upper closure plate (3) having a suction port (9) , said suction port communicating with said channel; a lower closure plate (4) having a discharge port ( 1⊘ ), said discharge port ( 1⊘ ) communicating with said channel (1) ; said upper closure plate (3) and a first plane surface of said rotor disk (5) facing said upper closure plate defining a first region (7) of close tolerance between said discharge port ( 1⊘ ) and said suction port (9) ; said lower closure plate (4) and a second plane surface opposed to said first plane surface of said rotor disk (5) facing said lower closure plate (4) defining a second region (8) of close tolerance between said discharge port ( 1⊘ ) and said suction port (9) ; a baffle (18) , said baffle being protruded from said plates (3,4) , characterized in that said annular grooved inner wall of said stator (2) has a substantially semicircular internal perimeter and that the lateral surface of rotor disk (5) has a substantially semicircular groove (12) , said baffle (18) extending into said groove of said rotor disk (5) and forming a third region of close tolerance (11) therewith, whereby said flow channel (1) has a cross-sectional area enlarged from said upper and lower closure plates (3,4) to the center of the channel along a direction parallel to the pump shaft (6) . A turbomolecular pump having a tangential flow pumping stage and axial flow pumping stage, said tangential flow pumping stage comprising: a rotor disk (5) secured to a pump shaft (6) and a stator (2) , said stator having an annular grooved inner wall receiving a lateral portion of said rotor disk (5) ; said lateral portion of said rotor disk (5) and said annular grooved inner wall of said stator (2) defining a flow channel (1) ; an upper closure plate (3) having a suction port (9) , said suction port communicating with said channel; a lower closure plate (4) having a discharge port ( 1⊘ ), said discharge port ( 1⊘ ) communicating with said channel (1) ; said upper closure plate (3) and a first plane surface of said rotor disk (5) facing said upper closure plate defining a first region (7) of close tolerance between said discharge port ( 1⊘ ) and said suction port (9) ; said lower closure plate (4) and a second plane surface opposed to said first plane surface of said rotor disk (5) facing said lower closure plate (4) defining a second region (8) of close tolerance between said discharge port ( 1⊘ ) and said suction port (9) ; a baffle (18) , said baffle being protruded from said plates (3,4) , characterized in that said annular grooved inner wall of said stator (2) has a substantially semicircular internal perimeter and that said rotor disk has a plane lateral surface, said baffle (18) extending towards said plane lateral surface of said rotor disk (5) and forming a third region of close tolerance (11) therewith, whereby said flow channel (1) has a cross-sectional area enlarged from said upper and lower closure plates (3,4) to the center of the channel along a direction parallel to the pump shaft (6) . A turbomolecular pump having a tangential flow pumping stage and axial flow pumping stage, said tangential flow pumping stage comprising: a rotor disk (5) secured to a pump shaft (6) and a stator (2) , said stator having an annular grooved inner wall receiving a lateral portion of said rotor disk (5) ; said lateral portion of said rotor disk (5) and said annular grooved inner wall of said stator (2) defining a flow channel (1) ; an upper closure plate (3) having a suction port (9) , said suction port communicating with said channel; a lower closure plate (4) having a discharge port ( 1⊘ ), said discharge port ( 1⊘ ) communicating with said channel (1) ; said upper closure plate (3) and a first plane surface of said rotor disk (5) facing said upper closure plate defining a first region (7) of close tolerance between said discharge port ( 1⊘ ) and said suction port (9) ; said lower closure plate (4) and a second plane surface opposed to said first plane surface of said rotor disk (5) facing said lower closure plate (4) defining a second region (8) of close tolerance between said discharge port ( 1⊘ ) and said suction port (9) ; a baffle (18) , said baffle being protruded from said plates (3,4) , characterized in that said annular grooved inner wall of said stator (2) has a substantially rectangular shape and that the lateral surface of rotor disk (5) has a substantially semicircular groove (12) , said baffle (18) extending into said groove of said rotor disk (5) and forming a third region of close tolerance (11) therewith, whereby said flow channel (1) has a cross-sectional area enlarged from said upper and lower closure plates (3,4) to the center of the channel along a direction parallel to the pump shaft (6) . The turbomolecular pump of claim 1 or 2 or 3 wherein said upper and lower closure plates are joined together by coupling of a downwardly extending edge (19) of upper closure plate (3) with a upwardly extending edge ( 2⊘ ) of lower closure plate (4) .

Inventors: HELMER JOHN C, LEVI GIAMPAOLO, HELMER, JOHN C., LEVI, GIAMPAOLO
Applicants: VARIAN ASSOCIATES, VARIAN ASSOCIATES, INC.
Application year: 1994
Main classification: F04D19
IPC codes: F04D19